The present invention relates to a position matching system for matching marks, which are provided on a web of packaging material with a pitch corresponding to the length of one container, to a reference position, and to packaging machines including the system and adapted to make the web of packing material into a tube, fill contents into the tube, transport the filled tube a distance at a time which distance corresponds to the length of one container, seal and sever the tube transversely thereof to form a pillowlike container, and eventually form the pillowlike container into a rectangular parallelepipedal container.
As disclosed, for example, in JP-B43-27194(1968), web position matching systems of the type mentioned and already known comprise sensor means for detecting the displacement of the mark from the reference position, and setting means for setting a usual amount of feed obtained by adding a predetermined amount of advance to a predetermined reference amount of feed corresponding to the length of one container when the displacement detected by the sensor means is smaller than a predetermined allowable displacement or setting a corrected amount of feed obtained by subtracting a predetermined amount of delay from the reference amount of feed when the detected displacement is not smaller than the allowable displacement.
The displacement of the mark from the reference position occurs frequently due, for example, to the slippage of the web during transport, disturbances such as variations in tension, or errors in the pitch of marks.
For example, if the mark pitch is shorter than the length of one container, the mark is displaced to a position downstream from the reference position, whereas if the mark pitch is longer than the length of one container, the mark is displaced to a position upstream from the reference position. Such a displacement occurs due not only to mark pitch errors but also to disturbances. For the convenience of description, however, the displacement will be handled herein as being attributable to an error in mark pitch.
With the conventional system, the amount of feed of the web is set in two steps, i.e., the usual amount of feed and the corrected amount of feed, which are repeated in a mode so that the marks will not be displaced from the reference position by more than an allowable amount. However, the system has the problem that the displacement, if great, is not absorbable or requires time for absorption.
Further when the amount of advance is set, for example, at +0.5 mm and the amount of delay at xe2x88x921.0 mm in the conventional system, and if the mark pitch is shorter than the reference amount of feed by 0.5 mm, the web will be fed apparently 1.0 mm more than the reference amount of feed at a time, and this difference will be barely absorbed with the set amount of delay of xe2x88x921.0 mm. Accordingly, if the mark pitch is shorter than the reference amount of feed by at least 0.5 mm, the displacement can not always be absorbed. Conversely if the mark pitch is 0.5 mm longer than the reference amount of feed, this difference can be barely absorbed by the set amount of advance of +0.5 mm, and if the mark pitch is more than 0.5 mm longer than the reference amount of feed, the difference is not absorbable.
An object of the present invention is to overcome the above problems and to provide a web position matching system which is adapted to absorb the displacement of marks reliably and within a short period of time even if the displacement is great and also packaging machines equipped with the system.
The present invention provides a web position matching system for matching marks provided on a web of packaging material with a pitch corresponding to the length of one container, to a reference position, the system comprising sensor means for detecting the displacement of the mark from the reference position, setting means for setting a usual amount of feed obtained by adding a predetermined amount of advance to a predetermined reference amount of feed corresponding to the length of one container when the displacement detected by the sensor means is smaller than a predetermined allowable displacement or setting a corrected amount of feed obtained by subtracting a predetermined amount of delay from the reference amount of feed when the detected displacement is not smaller than the allowable displacement, and means for correcting the usual amount of feed and the corrected amount of feed based on a pattern of frequencies with which the usual amount of feed and the corrected amount of feed are set by the setting means.
With the web position matching system of the invention, the amount of feed of the web is set in two steps, i.e., the usual amount of feed and the corrected amount of feed, and is so set as to correct the usual amount of feed and the corrected amount of feed based on a pattern of frequencies with which the usual amount of feed and the corrected amount of feed are set by the setting means. Accordingly, the amount of feed of the web is set in at least three steps. This makes it possible to control the amount of feed of the web finely and to absorb the displacement of marks reliably within a short period of time even if the displacement is great.
The pattern may be judged based on the deviation of the apparent amount of feed of the mark due, for example, to an error in mark pitch from the usual amount of feed.
Preferably, the usual amount of feed and the corrected amount of feed are corrected by zero when the apparent amount of feed is equal to the usual amount of feed, the usual amount of feed and the corrected amount of feed are corrected by subtracting a predetermined correcting amount when the apparent amount of feed is in excess of the usual amount of feed, or the usual amount of feed and the corrected amount of feed are corrected by adding a predetermined correcting amount when the apparent amount of feed is less than the usual amount of feed.
The mode of feeding is judged as being a normal mode when the number of times the setting means actually sets the usual amount of feed and the corrected amount of feed after the time when the corrected amount of feed is set previously and until the corrected amount of feed is set currently is equal to a predetermined number of times, the feeding mode is judged as being a down mode when the number of times of actual settings is in excess of the predetermined number of times, or the feeding mode is judged as being an up mode when the number of times of actual settings is less than the predetermined number of times, the correcting means being operable to correct the usual amount of feed and the corrected amount of feed by zero in the normal mode, to correct the usual amount of feed and the corrected amount of feed by adding a predetermined correcting amount in the down mode, or to correct the usual amount of feed and the corrected amount of feed by subtracting a predetermined correcting amount in the up mode. In this case, when the mark pitch is equal to the predetermined reference amount of feed, the feeding mode is judges as being the normal mode, and the web is fed by the usual amount of feed and the corrected amount of feed, as zero-corrected. If the mark pitch is in excess of the reference amount of feed, the feeding mode is judged as being the down mode, and the web is fed by the usual amount of feed and the corrected amount of feed which are corrected by subtraction. If the mark pitch is less than the reference amount of feed, the feeding mode is judged as being the up mode, and the web is fed by the usual amount of feed and the corrected amount of feed, as corrected by addition. Thus, the differences in the mark pitch can be handled widely by corrected amounts.
The present invention provides a packaging machine comprising a tube forming device for forming a tube from a web bearing marks thereon with a pitch corresponding to the length of one container, a filling device for filling the tube with contents, and a container forming device for forming pillowlike containers by sealing and severing the filled tube transversely thereof while transporting the tube a distance at a time which distance corresponds to the length of one container, the container forming device comprising a pair of openable flaps for folding a pair of triangular ears in forming the pillowlike container, a drive mechanism for opening the flaps to an adjustable degree and closing the flaps, and a web position matching system for controlling the drive mechanism so as to match the mark to a reference position, the drive mechanism having first and second fluid pressure cylinders, the first fluid pressure cylinder being operable to open the flaps to a first degree and close the flaps, the second fluid pressure cylinder being operable to open the flaps to a second degree resulting from the first degree by correction and close the flaps.
With the packaging machine of the invention, the flaps are opened over the wide ranges of first and second opening degrees so as to control the feed of the web in widely varying amounts.
When the first and second fluid pressure cylinders are so connected as to provide power transmission paths in series, one of the first and second opening degrees is variable with the other opening degree fixed to facilitate the control of the amount of feed of the web.
Preferably, the packaging machine is provided with the web position matching system described.